The present invention generally relates to devices for removing undesirable deposits from the lumen of a blood vessel or of a stent positioned in a blood vessel, and more particularly, to atherectomy devices.
Vascular diseases, such as atherosclerosis and the like, have become quite prevalent in the modern day. These diseases may manifest themselves in a number of ways, often requiring different forms or methods of treatment for curing the adverse effects of the diseases. Vascular diseases, for example, may take the form of deposits or growths in a patient""s vasculature which may restrict, in the case of a partial occlusion, or, stop, in the case of a total occlusion, blood flow to a certain portion of the patient""s body. This can be particularly serious if, for example, such an occlusion occurs in a portion of the vasculature that supplies vital organs with blood or other necessary fluids.
To treat these diseases, a number of different therapies have been developed. While a number of effective invasive therapies are available, it is desired to develop non-invasive therapies as well. Non-invasive therapies may be more desirable because of the possibility of decreased chances of infection, reduced post-operative pain, and less post-operative rehabilitation. Drug therapy is one type of non-invasive therapy developed for treating vascular diseases. Clot-dissolving drugs have been employed to help break up blood clots which may be blocking a particular vascular lumen. Other drug therapies are also available. Further, non-invasive intravascular treatments exist that are not only pharmaceutical, but also physically revascularize lumens. Two examples of such intravascular therapies are balloon angioplasty and atherectomy, both of which physically revascularize a portion of a patient""s vasculature.
Balloon angioplasty is a procedure wherein a balloon catheter is inserted intravascularly into a patient through a relatively small puncture, which may be located proximate the groin, and intravascularly navigated by a treating physician to the occluded vascular site. The balloon catheter includes a balloon or dilating member which is placed adjacent the vascular occlusion and is then inflated. Intravascular inflation of the dilating member by sufficient pressures, on the order of 5 to 12 atmospheres or so, causes the balloon to displace the occluding matter to revascularize the occluded lumen and thereby restore substantially normal blood flow through the revascularized portion of the vasculature. It should be recognized that this procedure does not remove the matter from the patient""s vasculature, but displaces and reforms it.
While balloon angioplasty is quite successful in substantially revascularizing many vascular lumens by reforming the occluding material, other occlusions may be difficult to treat with angioplasty. Specifically, some intravascular occlusions may be composed of an irregular, loose or heavily calcified material which may extend relatively far along a vessel or may extend adjacent a side branching vessel, and thus may not be prone or susceptible to angioplastic treatment. Even if angioplasty is successful, there is a chance that the occlusion may recur. Recurrence of an occlusion may require repeated or alternative treatments given at the same intravascular site.
A relatively new technique to reduce the recurrence of occlusion after a balloon angioplasty procedure involves providing a stent at the revascularized site. A stent is typically a hollow tube, typically braided, that can be inserted into the vascular of a patient in a compressed form. Once properly positioned at a desired site, the stent is expanded to hold the vessel open in an attempt to prevent restenosis. While this technique can help maintain blood flow past the site, it has been found that the occluding material often migrates through the interstices of the stent braid, and may again occlude the vessel. This phenomenon is sometimes referred to as interstitial hyperplasia.
Accordingly, attempts have been made to develop other alternative mechanical methods of non-invasive, intravascular treatment in an effort to provide another way of revascularizing an occluded vessel and of restoring blood flow through the relevant vasculature. These alternative treatments may have particular utility with certain vascular occlusions, or may provide added benefits to a patient when combined with balloon angioplasty, drug and/or stent therapies.
One such alternative mechanical treatment method involves removal, not displacement of the material occluding a vascular lumen. Such treatment devices, sometimes referred to as atherectomy devices, use a variety of material removal means, such as rotating cutters or ablaters for example, to remove the occluding material. (The term xe2x80x9catherectomy devicexe2x80x9d as used throughout the specification refers to ablation devices for use in any portion of a patient""s vasculature. Thus, while the atherectomy devices provided in accordance with preferred embodiments of the present invention are well suited for use in the coronary arteries, their use is not limited to the coronary arteries.) The material removal device is typically rotated via a drive shaft that extends out of the vascular of the patient and to an electric motor.
In operation, an atherectomy device is typically advanced over a guide wire placed in vivo until the material removal device is positioned just proximal to the occluded site. The motor is used to rotate the drive shaft and the material removal device, and the material removal device is moved through the occluded vessel. The material removal device removes the material from the vessel, rather than merely displacing or reforming the material as in a balloon angioplasty procedure.
A potentially negative characteristic for all atherectomy devices is the unwanted perforation of a vessel wall by the material removal device. This can occur when the material removal device improperly engages the vessel wall, for example when the material removal device is not oriented substantially parallel to the axis of the vessel. In this situation, the material removal device (e.g., cutter or abrasive ablater) may improperly engage the vessel wall and cause unwanted damage thereto.
Similarly, an atherectomy device may cause damage to an in vivo stent when used to remove occluding material from within the stent caused by, for example, interstitial hyperplasia. Even a properly oriented material removal device may damage a stent. If the cutter or ablater of a typical atherectomy device engages a stent, particulates of the stent and/or material removal device may be removed and introduced into the vasculature of the patient, which can cause complications. To reduce this risk, the material removal device typically has an outer diameter that is substantially less than the inner diameter of the stent. It is believed that this may reduce the risk that the material removal device will engage and thus damage, the stent. A limitation of this approach is that a substantial gap typically must be provided between the material removal device and the stent. This may reduce the amount of occluding material that can be removed from within the stent. Accordingly, the stent will likely become occluded again sooner than if the outer diameter of the material removal device could more closely match the inner diameter of the stent, and remove more of the occluding material.
Given the above-discussed considerations, it would be desirable to provide an atherectomy device that can reduce the risk of damage to a vessel wall and/or an in vivo stent. In particular, it would be advantageous to provide an atherectomy device that can align the burr cutting action with a path through the stenosed vessel while removing unwanted material and yet not cause excessive wear on the vessel walls. The present invention fulfills these needs, and provides further related advantages.
The present invention overcomes many of the disadvantages of the prior art by providing an atherectomy device that may reduce the risk of damage to a vessel wall and/or an in vivo stent. In one embodiment of the present invention, an atherectomy device is provided that has a rotatable ablation burr attached to the distal end of a flexible drive shaft. The ablation burr can have generally elliptical proximal and distal shoulders and a generally cylindrical material removal portion therebetween. In a preferred embodiment, the material removal portion is substantially cylindrical and is recessed relative to the shoulders. In a preferred embodiment, the material removal portion contains abrasive material such as diamond grit adhered to the outer surface.
The proximal and distal shoulders are substantially less abrasive than the material removal portion. The shoulders are tapered and act to align the burr along a path through the stenosed vessel. Aligning the burr allows an unwanted, projecting deposit to be presented to the material removal portion while the less abrasive shoulders are presented to the vessel wall. The shoulders can serve to re-align the burr when the burr assumes a cant due to a tortuous path through a stenosed vessel.
In another embodiment of the present invention, an atherectomy device is provided that has a flexible drive shaft with an ablation burr attached to the distal end thereof. The ablation burr is preferably generally elliptical in shape except for a concave shaped leading surface. An abrasive grit is then disposed on the concave shaped leading surface. Extending distally from the concave shaped leading surface is a distal tip portion, and extending proximally from the concave shaped leading surface is a convex shaped portion. Both the distal tip portion and the convex shaped portion have non-abrasive surfaces.
In this configuration, the abrasive grit is effectively prevented from engaging a vessel wall regardless of the orientation of the ablation burr within the vessel. That is, the non-abrasive surfaces of the distal tip and the convex shaped portion will tend to engage the vessel wall before the concave shaped leading surface, and may effectively prevent the abrasive grit of the concave shaped leading surface from engaging the vessel wall. To further reduce the friction between the ablation burr and the vessel wall, the convex shaped portion may have a number of dimples formed therein.
It is recognized that the benefits of this embodiment may equally apply when the ablation burr is used to remove unwanted deposits from within a stent (e.g., interstitial hyperplasia). In this application, however, the present invention may effectively prevent the abrasive grit on the concave shaped leading surface from engaging the stent, rather than the interstitial hyperplasia. This may reduce the risk of damage to the stent.
In another embodiment of the present invention, the ablation burr may include an outer surface which is generally non-abrasive, but has a number of depressions therein forming a number of depressed surfaces. An abrasive is provided only on the depressed surfaces. In this configuration, all of the abrasive is positioned just below the outer surface of the ablation burr. Accordingly, only the non-abrasive outer surface of the ablation burr contacts the stent. The occluding material within the stent, however, may enter the depressions and become ablated. Preferably, the depressions form a number of depressed flutes in the outer surface of the ablation burr.
In another embodiment of the present invention, the ablation burr has a generally elliptical outer surface with a selected portion of the outer surface having an abrasive coating. The abrasive coating is formed from a material that is softer than the material used to form the stent. Accordingly, the abrasive may not damage the stent. In a preferred embodiment, the abrasive includes a number of chips or a grit that comprises plastic or some other malleable material that is softer than the material used to form the stent. It is known that stents are typically formed from stainless steel or Nitinol.
In another embodiment of the present invention, the atherectomy device includes a cutter device rather than an ablation device on distal end thereof. The cutter device may be generally elliptical in shape, and may have a number of cutter blades on at least a leading surface thereof. In this embodiment, at least a portion of selected cutter blades are made from a material that is softer than the material used to form the stent. As indicated above, stents are typically made from either stainless steel or Nitinol. In the present embodiment, it is contemplated that the cutter blades can be made from a softer material such as aluminum, titanium or annealed stainless steel. These materials are advantageous in that they are very ductile. It is contemplated, however, that the cutting blades may be surface hardened by oxidizing, nitriding, carbonizing or by some other process to maintain a sharp cutting edge. A sharp cutting edge is often important to minimize the particle size of the ablated atheroma. If the burr contacts the stent, the underlying ductile burr material preferably plastically deforms, thus preventing particle generation from either the burr or the stent.
An advantage of all of these embodiments is that the material removal device (e.g., cutter or ablater) can have an outer diameter that more closely matches the inner diameter of a stent. In prior atherectomy devices, the material removal device typically had an outer diameter that was substantially less than the inner diameter of the stent to reduce the risk that the material removal device will engage, and thus damage, the stent. However, in the present invention, appropriate portions of the material removal devices are formed from a softer material than the stent. This may allow the material removal device to engage the stent without substantially damaging the stent. Accordingly, the present invention may allow the material removal device to have an outer diameter that more closely matches the inner diameter of the stent, which may allow the material removal to remove more of the occluding matter from the stent.
In another preferred embodiment of the present invention, the ablation device includes a burr having an inner circumferential rim at the distal end of the burr and an outer circumferential rim that is spaced longitudinally from the inner circumferential rim by a first distance. The outer circumferential rim defines a maximum diameter of the burr. A leading surface extends between the inner and outer circumferential rims in a substantially uniform, concave manner. An abrasive is provided on the leading surface, and the burr is coupled to a drive shaft that selectively rotates the burr. Furthermore, the outer circumferential rim is preferably non-abrasive and is convex in profile.
In another embodiment of the present invention, a wire extends co-axially through the burr, such that a first distal end of the wire extends out of the body, distal to the first annular edge. An abrasive tip is coupled to a distal end of the wire and is selectively rotated to ablate unwanted deposits.
In another embodiment of the present invention, the burr is made of a compressible, elastomeric material. The burr is positioned in a compressed condition within a guide catheter for positioning at a desired location within a patient""s vasculature. Once the guide catheter is at the desired location, the burr is pushed out of the catheter, allowing it to expand to a operational expanded condition.
In another embodiment to the present invention, an ablation device is advanced to a desired site within a patient""s vasculature over a guide wire having a bearing provided at a distal region of the guide wire. The bearing has a dynamic member that acts as a bumper and rotates when the ablation device is advanced to the distal region of the guide wire and contacts the dynamic member. The guide wire having the bearing is advanced through the patient""s vasculature until the bearing is positioned just distal of the unwanted deposit or lesion.
In another embodiment of the invention, an atherectomy burr having a relatively flat leading surface includes one or more aspiration ports through which particles ablated from a patient""s vessel may be removed. The burr is driven with a substantially sealed drive shaft that may include a section of heat shrink tubing sandwiched between filar windings. The proximal end of the sealed drive shaft is connected to a regular atherectomy drive shaft through a coupling. The coupling includes a window that rotates with the burr. Surrounding the conventional drive shaft and coupling is a sheath. The proximal end of the sheath is connected to a source of vacuum that draws particles aspirated from the patient through the front face of the burr, the sealed drive shaft and through the window of the coupling. The particles then are drawn along the lumen of the shaft to a filter that is in line with the source of vacuum.